is lossless MP2 to MPC conversion possible?, goal: reduce bitrate of existing files. Options

[smack]

The wiki articles on Musepack say that it's extended from the MP2 codec, e.g. Hydrogenaudio Wiki and Wikipedia

Does anybody know if it's feasible to losslessly convert MP2 files into MPC files?
If yes, does such a program already exist? (similar to mpc2sv8, the Musepack SV7 to SV8 converter)

Motivation: I'm asking this because I have many gigabytes of MP2 files stored on my hard disks. These are captured DVB radio broadcasts in 320kbps 48kHz stereo MPEG-1 Layer II format. I would like to save some storage space here and hope that Musepack with its more efficient lossless coding method can produce smaller files than MP2.

[--pv--]

If such a tool ever existed you won't be able to save space and do a losless transcode at the same time I am afraid.
If you want to affect size you need to affect bitrate of the files I think. And if you'll affect bitrate you have to do encoding.

[r2d]

Does anybody know if it's feasible to losslessly convert MP2 files into MPC files?
If yes, does such a program already exist? (similar to mpc2sv8, the Musepack SV7 to SV8 converter)

Yes, it is probably possible to losslessly convert from MP2 files to musepack. But even if the entropy coding is better, I don't think you will be able to gain more than 20% of the file size.
I don't know any program that do that (but I may be able to help you if you want to do it).

[Antonski]

Saving 20% of the size is not bad at all! This would be the first case of lossless transcoding of a lossy format (since the vorbis bit peeling was never realized after all). Such tool would have a similar functionality as the lovely mp3packer, but for mp2.

[SebastianG]

Saving 20% of the size is not bad at all! This would be the first case of lossless transcoding of a lossy format (since the vorbis bit peeling was never realized after all). Such tool would have a similar functionality as the lovely mp3packer, but for mp2.

I don't know if it's really possible (depends on how much MPC differs from MP2). But given that MPC uses the same filterbank and framesize as MP2 it might actually work. And if it is possible it's just like unpacking a TAR (that has no compression at all) and repacking it with something like 7zip. Nothing special, really.

To see if it's possible someone needs to check whether the whole scale factor & quantization part of MPC is MP2-compatible.

Cheers,
SG

This post has been edited by SebastianG: Sep 13 2009, 18:28

[smack]

Yes, it is probably possible to losslessly convert from MP2 files to musepack. But even if the entropy coding is better, I don't think you will be able to gain more than 20% of the file size.
I don't know any program that do that (but I may be able to help you if you want to do it).

That's good news! I mean, it would have been even better if such a conversion program already existed. Anyway, I'm going to start by exploring mpc2sv8.

To see if it's possible someone needs to check whether the whole scale factor & quantization part of MPC is MP2-compatible.

Good point. Going to compare mp2 and mpc decoders to find this out.

Well, at least I hope to accomplish that while my motivation lasts...

[smack]

The codecs use different scale factor steps:
MPC: 10**(5/63) = 1.58 dB
MP2: 2**(1/3) = 2.01 dB

There are some more differences, like the "grouped samples" in MP2 (3-in-1) which MPC doesn't seem to have.

Hm, does that mean that a lossless conversion from MP2 to MPC is impossible?

[smack]

I'm still unsure whether the lossless conversion is possible or not.

By chance I've just found this ancient thread where Frank Klemm stated that he had modified an MPC encoder to emit MP2 bitstreams. Apparently it was never released to the public.

What does that tell us about the internal differences between the two codecs? Can the bitstreams be converted? (mp2 <-> mpc)

Does anybody know more about this?

[а.п.т.]

By chance I've just found this ancient thread where Frank Klemm stated that he had modified an MPC encoder to emit MP2 bitstreams. Apparently it was never released to the public.

What does that tell us about the internal differences between the two codecs? Can the bitstreams be converted? (mp2 <-> mpc)

Does anybody know more about this?

Maybe Franc Klemm is the one who can throw some light on this?

This post has been edited by а.п.т.: Oct 1 2009, 09:17

[Jan S.]

By chance I've just found this ancient thread where Frank Klemm stated that he had modified an MPC encoder to emit MP2 bitstreams. Apparently it was never released to the public.

What does that tell us about the internal differences between the two codecs? Can the bitstreams be converted? (mp2 <-> mpc)

Does anybody know more about this?

Maybe Franc Klemm is the one who can throw some light on this?

Unfortunately as far as we know he doesn't read this forum anymore.